Solvent extraction of hydrocarbons with fluorinated aliphatic carboxylic acids



A F. N. RUEHLEN SOLVENT EXTRAC v TION OF' HYDROCARBONS WITH FLUORINATEDALIPHATIC CARBOXYLIC ACIDS Filed July 28, 1950 oct. 21, 1952 INVENTOR.F"N RUEHLEN BY E A T TQRNE KS Patented Oct. 21, `1952 SOLVENTEXTRACTIONOF HY DRQCARBONS WITH FLUORINATED ALIPHATIC CAR- BOXYLIC ACIDS ForrestN. `Ruehlen, Bartlesville, -kla.,assignor to` Phillips` PetroleumCompany, `a corporation of Delaware Application July 2s,

This invention relates to a novel-class of selective solvents, In one ofits more specific aspects it relatesto the separation of members ofdifferent or the same hydrocarbon groups. In one specific embodiment theinvention relates to 19m-scritti Nq. 176,466

the separation of aromatics, isoparafiins, n-par-` The process ofselective solvent` extraction is` not new. 'Numerousmixtures especiallyof organic compoundshave been separated by solvents in which thediierence in the solubility of the components of themixture al solventis utilized to eiect the separation. For example, the high viscosityindex components of a lubricating oil have been separated from the lowV. I. components by extraction of the latter `with phenol, sulfurdioxide, hydrofluoric acid, and numerous other solvents. Close-boilingmixtures and azeotropic mixtures of organic and inorganic mixtures mayalso be effectively separated by the` solvent extraction process Wheresuch separation cannot be made by ordinary fractionation. Because of theeffectiveness of this process Where many other processes areineffective, solvent extraction is most useful. v

In general, the process of selective solvent extraction is practiced bycontacting the mixture to be separated with a selective solventwhich hasa limited solubility for the components of the mixture, separating thesolvent phase fand the rainate phase, removing the solventlfrorn eachphase, and separately recovering the non-solvent portion of each phase.Both single-stage contacting and multi-stage contacting have been used,their use being determined by the ease of separation and by the degreeof separation desired. i

An object of this invention is to provide a new group of selectivesolvents. Another object is to provide a new group oi selective solventsfor the separation of` members of the same or different hydrocarbongroups.

Another object of this invention is to provide a new class of selectivesolvents for the separation ofaromatics from isoparains, and/ornparaiiinsyand/or cycloparains.

Another object of this invention is to provide a new class of selectivesolvents forthe separation of isoparaiiins from n-parains and/orcycloparains..

`Another object of this invention is to provide a new class of selectivesolvents for theseparaseparated hydrocarbons tion of ,-n-parafns fromcycloparafns.

13o1aiins. (C1. 19e- 14.35 T

A further object is to `provide a new group of solvents for theseparation of different hydro-- carbons of the same hydrocarbon group. i

' Still another object is to provide a method for the separation ofaromatics from isoparainns and/ or n-parans and/or cycloparains,isoparaiiins from n-paraiiins and/ or cycloparafiins, and n-paraiiinsfrom cycloparaiiins. i

Other objects and advantages of myinvention will be apparenttooneskilled `in the art from the following discussion and disclosure..`

I have `discovered a new Vclass ofV selective sol-j vents eiective forthe separation of hydrocar-- bons bytype and the separation ofhydrocar'bons within a type. In the latter case thecompound of lowestboiling point is th'emost-soluble.v `These solvents are the aliphaticcarboxylic Eacids i in which the aliphatic group is completelyfluorinated. Inparticular, these acids may contain not `more than '1``carbon atoms in the aliphatic group. These solvents are effective forthe sep"- aration of isoparafdns, n-paraiiins and/or cycloparafns `andaromatics, isoparailins and `nparans and/or cycloparains, andn-parariins and cycloparaiiins, and evenmembers of the samel and '125 F.As the process is carried out in liquid phase, pressure sunicient tomaintain substantially liquidv phase is employed in the con-` tactingzone. The ratio of solvent to hydrocarbon is ordinarilybetween 20:1 toi510, although in some instances ratiosoutside these limits may be used.

.This process can be carried out by contacting" the solvent andhydrocarbon mixture in a packed tower, a` system of pumps and settlingchambers or other effective means. The extract and rafiinate phases maythen be freed of solvent by a system of fractionation, whereby thesolvent and separated `hydrocarbons are `recovered'and;.fthe withdrawnas products ofthe process.` i

The solvents particularly included in the process of this invention arethe `alkyl carboxylic acids in which the alkyl group is completelyfluorinated. Examples of these acids are tri fluoroaceticI acid, whose'boiling point is about F., and heptaluorobutyric acid,'whose`boil` ofsole homologous series such as heptaluoroisobutyric acid,nonafluoro-Z-methylbutanoic acid, and undecafluorohexanoic acid.

Although it is generally preferred to utilize the perfluoroacidscontaining not more than 7 carbon atoms in the aliphatic group, I do notwish to be limited to these acids alone, since heavier acids containingmore than 7 carbon atoms can be used, particularly in admixture with thelower boiling acids.

Though the solvents of this invention are each useful for separation ofa great number of specic mixtures of quite different boiling ranges, theindividual solvents are not necessarily equivalent for any oneseparation. As the number of separations possible by the process of thisinvention is quite large, some experimentation with several individualsolvents may be desirable in order to determine themost satisfactoryone. In a few-isolated cases a particular periluoroacid will beinfinitely miscible with one of the hydrocarbons to be separated. Suchsolubility characteristics limit the separation obtainable with thissolvent in the extraction of such a specific hydrocarbon mixture.However, a perfluoroacid of greater or lesser number of carbon atoms permolecule, or sometimes merely a different chain configuration, will havesatisfactory solubility characteristics to effect this separation.

As an illustration of the previous paragraph, I` have found thattriuoroacetic acid and benzene are iniinitely miscible even at quite lowternperatures. Therefore, complete separation of a benzene-normal hexanemixture with trifluoroacetic acid is not possible, although partialseparation is possible. However, these two hydrocarbons can be separatedby use of the heptauorobutyric acid, for this acid and either of thesehydrocarbons are of limited miscibility even at 75 F.

Refer now to the attached drawing, which is a schematic iiow diagram ofone method for carrying out an extraction process utilizing my novelsolvents. Various additional valves, pumps, and

other conventional equipment necessary for the K practice of thisinvention will be familiar to one skilled in the art and have beenomitted from the drawing for the sake of clarity. Although the drawingrepresents one embodiment of my invention, various minor changes may bemade in f adapting the process to the various conditions within thescope of the invention.

The attached drawing is a schematic diagram of one specific embodimentof this invention. In

thisembodiment normal nonane and cumene are .C

separated by the use of a periluoroacid as the selective solvent. Amixture of normal nonane and cumene is introduced to the system throughline I to extractor II. The solvent acid is introduced at the top ofextractor II from a source to be described, and reflux cumene isintroduced at the bottom of the extractor through line'3 I. The solventpasses downward through the extractor and extracts cumene from therising hydrocarbon `and a liquid stream of nonane saturated with solventis withdrawn from the top of the extractorthrough line I2 and introducedto fractionator I3. In the fractionator a mixture of normal nonane andsolvent is carried overhead and the nonane substantially free of solventis withdrawn'as a kettle product through line 22 and is conducted tostorage, not shown. The overhead mixture is withdrawn through line I4and admixed with a similar stream from line I9 from asourcetobedescribed. The total streamislthen` conducted to separator I5wherein an upper phase predominating in hydrocarbon and a lower phase ofhigh solvent content separate. The upper phase is conducted through lineIl back to line I2, then following a previously described route. Thelower phase is removed through line I6 and conducted to fractionator I8wherefrom a mixture of normal nonane and solvent is removed through lineI9 and conducted to line I4, then following a previously describedroute. Substantially pure solvent is removed as a kettle product throughline 20. Alternatively, the material in line I6 withdrawn from separatorI5 may be passed directly to line 25 by means not shown, thus by-passingfractionator I8.

The extract phase is removed from extractor I I through line 23 and isconducted to fractionator 24. In this fractionator a mixture of cumeneand solvent is separated as an overhead product and removed through line26, a similar mixture is added to this stream through line 29 from asource to be described and the total stream conducted to separator 2 6.The liquid mixture separates herein into an upper phase predominatinghigh proportion of solvent. The upper phase is removed from separator 26through line 2l and conducted to fractionator 28 wherein an overheadproduct mixture of cumene and solvent is separated, removed through line29 and conducted to line 25, then following a previously describedroute. The lower phase in separator 26 is removed through line 32 andconducted back to line 23, joining a similar stream there and` followinga previously described route.

The kettle product of fractionator 24 is substantially pure solvent acidand is removed through line 34. The solvent carried by line 20 is joinedby a make-up solvent stream added through line 2| and the total streamadded tov line 34, the entire solvent stream then conducted through line34 and introduced to extractor I I as previously described. f

The kettle product of fractionator 28, which is substantially solventfree cumene, is removed through line Si) and a portion passed throughline 3l to the lower. portion of extractor II as refiux. The remainderof the stream is conducted through line 30 to storage as a product ofthe process.

The advantages of this invention are illustrated in the followingexample. and their proportions and other specific ingredients arepresented as being typical and should not be construed to limit theinvention unduly.

The above example clearly shows the high selectivity of the solvents ofmy invention for aromatics when in admixture with parains. It also showsa very outstanding selectivity for isoparains over n-paraflins andn-parafiinsovei.

The reactants cycloparafns.

From the data it is also apparent due to the very high solubility foraromatics that aromatics are preferentially dissolved when in admixturewith cycloparafns. Thus, while the expected selectivity would be foraromatics over paraiiins and for cycloparafns over kopen chainparaiiins, the above data show that the `latter selectivity is actuallyreversed.

tracting a mixture of hydrocarbons with at least one aliphaticcarboxylic acid in which the aliphatic group is completely iiuorinated.

2. A method for the separation of a hydrocarbon mixture containingaromatic, isoparainic, n-parainic and cycloparafiinic hydrocarboncomponents which comprises solvent extracting said mixture with at leastone aliphatic `car boxylic acid in which the aliphatic group iscompletely iluorinated and recovering an extract phase enriched withrespect to at least one of said hydrocarbon components.

3. A method according to `claim 2 wherein the aliphatic group of thecarboxylicacid contains not more than 7 carbon atoms permolecule.

4. A method according to claim 2 wherein the extraction processiscarried out at a'temperature of 0 to 150 F. and at a sufcient pressureto maintain liquid phase. j

5. A method according to claim2 wherein the aliphatic carboxylic acidthe aliphatic group of which is completely fluorinated, and carrying outthe separation at a temperature in the range of 0 to 150 F., in liquidphase, and with a ratio of solvent to hydrocarbon mixture in the rangeof i 9. A method according to claim 8 wherein .the separation is carriedout at a temperature in the range of 50 to 125 F.

10. A method for the separation of a `hydro` carbon mixture containingaromatic `and parafinic hydrocarbons which comprises solvent extractingsaid mixture with at least one aliphatic carboxylic acid in which thealiphatic group is completely iiuorinated and recovering an extractphase'enriched withrespect to said aromatic component.

' 11. A method for the separation of a hydroi carbon mixture containingisoparainic and n-parailinic hydrocarbon components which comprisessolvent extracting saidmixture with at least one aliphatic carboxylicacid in `which y the aliphatic group is completely uorinated and`recovering an extract phase enriched with respect to said isoparafliniccomponent.

12. A method for the separation of a hydro-` carbon mixture containingn-parainnic and cycloparaiinic hydrocarbon component whicheomprisessolvent extracting said mixture with spect to said parafniccomponent.

extraction process is carriedout'at a temperature in the range of 50 to125 F., a pressure suiiicient to maintain liquid phase, and with a ratioof solvent to hydrocarbons in the range of 20,:1 to 1:10. y

6. ,A process according to claim 5 wherein the solvent extraction iscarried out in countercurrent iiow of solvent and mixture .to beextracted.

'7. A method for the separation of aromatics from isoparaflins,n-parafns, and cycloparaiiins, isoparains from n-parains andcycloparafilns, and n-parains from cycloparairlns, which comprisescontacting a mixture to be separated with at least one aliphaticcarboxylic acid in which the aliphatic group is completely uorinated.

8. A method for the separation of a hydrocarbon mixture containingaromatic, isoparamnic, n-paraiinic and cycloparafnic hydrocarboncomponents, which comprises contacting said 5 mixture with a solventcomprising at least one 13. A method for' the separation ofhydrocarbonmixture containing aromatic `and cycloparafnic hydrocarbon componentswhich comprises solvent extractingsaid mixture with at least onealiphatic carboxylic 'acid in which the aliphatic group is completelyfluorinated and recovering Van extract phase enriched with respect tosaid aromatic component.

. FORREST N. RUEHLEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. A METHOD FOR THE LIQUID PHASE SEPARATION OF HYDROCARBONS WHICHCOMPRISES SOLVENT EXTRACTING A MIXTURE OF HYDROCARBONS WITH AT LEAST ONEALIPHATIC CARBOXYLIC ACID IN WHICH THE ALIPHATIC GROUP IS COMPLETELYFLUORINATED.